Base-pairing in dna involves acid-base reaction ionic bonds hydrogen bonds covalent bonds

The answer is hydrogen bonds.

In the DNA double helix structure nitrogen atoms are chemically bonded to hydrogen atoms. Given that nitgrogen atoms are more electronegative than hydrogen atoms, hydrogen atoms in a base-pairing will bear a partial positive charge.

That partial positive charge is atracted to the oxygen atoms (which are also more electronegative than hydrogen atoms) in the same base pairing in DNA.

That atraction constitutes the hydrogen bond.

Because electrons have negligible mass, to account for the mass of the isotope, there must be 16 neutrons, 16 neutrally charged, massive, fundamental particles present in the sulfur nucleus. and thus finally, if we have the 32s2− ion, there are 18 electrons, 16 protons, and 16 neutrons.